Quick answer
Distance ≈ (RTT ÷ 2) × signal speed, where speed is a fraction of the speed of light. A 20 ms round trip at 0.67c is about 2,008.6 km (1,248.1 miles) one way.
Enter the round-trip latency and the signal speed as a fraction of c. The calculator returns an approximate distance.
Related tools: IP Subnet Calculator: IPv4 network, broadcast, mask and host range from an address and CIDR prefix. Download Time Calculator: Time to download a file at a given speed. Bandwidth Calculator: Bandwidth needed to move a file in a given time.
How to use the Latency to Distance Calculator
- Enter round-trip latency (ms) (above 0).
- Enter signal speed as a fraction of c (between 0 and 1). It starts at 0.67.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Round-trip latency | A number, in ms | > 0 |
| Signal speed as a fraction of c | A number | > 0, ≤ 1, starts at 0.67 |
Formula and method
Formula
distance = (RTT ÷ 2) × v, v = fraction × c
IEEE-754 double precision; shown to the decimals indicated.
Optical fiber carries signals at roughly two thirds of c; routing and equipment delay make real paths longer.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Round-trip latency = 20; Signal speed as a fraction of c = 0.67.
| Result | Value |
|---|---|
| Approximate distance | 2,008.6 km |
| In miles | 1,248.1 |
Example 2
Inputs: Round-trip latency = 100; Signal speed as a fraction of c = 0.68.
| Result | Value |
|---|---|
| Approximate distance | 10,192.9 km |
| In miles | 6,333.6 |
The first line is the headline result (approximate distance). Below it the latency to Distance Calculator lists in miles, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Why 0.67
Light in optical fibre travels at about two-thirds of its vacuum speed, roughly 200,000 km/s. Half of 20 ms is 10 ms, which covers 2,000 km.
An upper bound
Real cable routes are longer than the straight line and routers add delay, so the true distance is shorter than the result. Treat it as a maximum.
How the result changes with round-trip latency
Holding every other input at the first worked example, this table changes only round-trip latency. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Round-trip latency | Approximate distance | In miles |
|---|---|---|
| 10 | 1,004.3 km | 624 |
| 20 | 2,008.6 km | 1,248.1 |
| 40 | 4,017.2 km | 2,496.2 |
| 80 | 8,034.4 km | 4,992.4 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Round-trip latency: entering "0" shows "Round-trip latency must be greater than 0." beside that field and no result.
- Signal speed as a fraction of c: entering "0" shows "Signal speed as a fraction of c must be greater than 0." beside that field and no result.
Choosing between the Latency to Distance Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [IP Subnet Calculator](/technology/ip-subnet-calculator/) | iPv4 address and cIDR prefix length | Network |
| [Download Time Calculator](/technology/download-time-calculator/) | file size, size unit and connection speed | Time |
| [Bandwidth Calculator](/technology/bandwidth-calculator/) | data size, size unit and time allowed | Bandwidth required |
| [Data Transfer Calculator](/technology/data-transfer-calculator/) | speed, speed unit and duration | Data transferred |
| [Network Throughput Calculator](/technology/network-throughput-calculator/) | tCP window size and round-trip time | Maximum throughput |
Background: networking and display
Network speeds are quoted in bits per second and file sizes in bytes, and a byte is 8 bits, so a 100 Mbps link moves at most 12.5 megabytes per second; real throughput is usually below the advertised rate. Pixel density is the diagonal in pixels divided by the diagonal in inches: a 1920×1080 display of 24 inches is about 92 pixels per inch, and a 3840×2160 display of 27 inches about 163.
Assumptions and limitations
- An upper bound on distance
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for round-trip latency and signal speed as a fraction of c to confirm this.
Frequently asked questions
How far is 1 ms of one-way delay?
About 200 km in fibre.
Is ping the same as RTT?
Yes, ping reports round-trip time.
Why is the result an upper bound?
Queueing and detours add time.
What does the Latency to Distance Calculator calculate?
Approximate one-way distance from round-trip latency. It returns Approximate distance and In miles.
What formula does the Latency to Distance Calculator use?
distance = (RTT ÷ 2) × v, v = fraction × c. Optical fiber carries signals at roughly two thirds of c; routing and equipment delay make real paths longer.
What do I need to enter in the latency to Distance Calculator?
You enter Round-trip latency (ms) and Signal speed as a fraction of c.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. An upper bound on distance.
What is an example of a latency to Distance result?
With round-trip latency 20 and signal speed as a fraction of c 0.67, the approximate distance is 2,008.6 km.
Where does the method come from?
The method follows: BIPM, The International System of Units (SI Brochure): speed of light in vacuum c = 299 792 458 m/s, exact.
Related calculators
- IP Subnet Calculator — IPv4 network, broadcast, mask and host range from an address and CIDR prefix.
- Download Time Calculator — Time to download a file at a given speed.
- Bandwidth Calculator — Bandwidth needed to move a file in a given time.
- Data Transfer Calculator — Amount of data moved at a speed over a time.
- Network Throughput Calculator — Maximum TCP throughput from window size and round-trip time.
- Packet Loss Calculator — Percentage of packets lost.
Sources
- BIPM, The International System of Units (SI Brochure): speed of light in vacuum c = 299 792 458 m/s, exact
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.